"He that will HEAR MY VOICE shall be MY SHEEP and him shall ye receive into the church and him will I also receive for behold THIS IS MY CHURCH." (Mosiah 26:21-22.)

Baptism in the Book of Mormon Church

There are only two sacraments or ordinances prescribed in the Book of Mormon - baptism and communion; and only one of those is required for salvation - Baptism of Repentance.

BAPTISM OF REPENTANCE

22 And again the Lord called others, and said unto them likewise; and he gave unto them power to baptize. And he said unto them: On this wise shall ye baptize; and there shall be no disputations among you.
23 Verily I say unto you, that whoso repenteth of his sins through your words, and desireth to be baptized in my name, on this wise shall ye baptize them—Behold, ye shall go down and stand in the water, and in my name shall ye baptize them.
24 And now behold, these are the words which ye shall say, calling them by name, saying:
25 Having authority given me of Jesus Christ, I baptize you in the name of the Father, and of the Son, and of the Holy Ghost. Amen.
26 And then shall ye immerse them in the water, and come forth again out of the water. (3 Nephi 11:22-28)

Parameters

1. Not for those who are without sin: not children, infants, the comatose, or the ignorant.

11 And their little children need no repentance, neither baptism. Behold, baptism is unto repentance to the fulfilling the commandments unto the remission of sins. (Moroni 8:11)

2. The sinner must have repented of their sins before being baptized.

BAPTISM OF ACCEPTANCE

There is another form of baptism which is used to show acceptance.

Of a Covenant

12 And now it came to pass that Alma took Helam, he being one of the first, and went and stood forth in the water, and cried, saying: O Lord, pour out thy Spirit upon thy servant, that he may do this work with holiness of heart.
13 And when he had said these words, the Spirit of the Lord was upon him, and he said: Helam, I baptize thee, having authority from the Almighty God, as a testimony that ye have entered into a covenant to serve him until you are dead as to the mortal body; and may the Spirit of the Lord be poured out upon you; and may he grant unto you eternal life, through the redemption of Christ, whom he has prepared from the foundation of the world. (Mosiah 18:12-13)

Of a Belief in Jesus

21 And the Lord said unto him: I give unto you power that ye shall baptize this people when I am again ascended into heaven. (3 Nephi 11:21)

"This people" had already been baptized before Jesus arrived - for repentance and the remission of sins:

23 Thus passed away the thirty and second year also. And Nephi did cry unto the people in the commencement of the thirty and third year; and he did preach unto them repentance and remission of sins.
24 Now I would have you to remember also, that there were none who were brought unto repentance who were not baptized with water.
25 Therefore, there were ordained of Nephi, men unto this ministry, that all such as should come unto them should be baptized with water, and this as a witness and a testimony before God, and unto the people, that they had repented and received a remission of their sins.
26 And there were many in the commencement of this year that were baptized unto repentance; and thus the more part of the year did pass away. (3 Nephi 7:23-26)

The baptism Jesus commanded the people to receive was for a belief in him:

33 And whoso believeth in me, and is baptized, the same shall be saved; and they are they who shall inherit the kingdom of God.34 And whoso believeth not in me, and is not baptized, shall be damned. (3 Nephi 11:33-34)

AUTHORITY

1. By God

Alma received authority straight from God, through the Holy Spirit:

12 And now it came to pass that Alma took Helam, he being one of the first, and went and stood forth in the water, and cried, saying: O Lord, pour out thy Spirit upon thy servant, that he may do this work with holiness of heart.
13 And when he had said these words, the Spirit of the Lord was upon him, and he said: Helam, I baptize thee, having authority from the Almighty God, (Mosiah 18:12-13)

Which was different from ecclesiastical or church authority which Alma received from Mosiah:

And it came to pass that King Mosiah granted unto Alma that he might establish churches throughout all the land of Zarahemla; and gave him power to ordain priests and teachers over every church. (Mosiah 25:19)

The difference was apparent when Jesus appeared to the Nephites and gave Nephi "power" which Nephi alread had:

25 Therefore, there were ordained of Nephi, men unto this ministry, that all such as should come unto them should be baptized with water, and this as a witness and a testimony before God, and unto the people, that they had repented and received a remission of their sins.
26 And there were many in the commencement of this year that were baptized unto repentance; and thus the more part of the year did pass away. (3 Nephi 7)

21 And the Lord said unto him: I give unto you power that ye shall baptize this people when I am again ascended into heaven. (3 Nephi 11)

2. By a Man Sent by God

Teachers and priests received their authority from a man - Alma, who received it from God.

13 And Alma established a church in the land of Sidom, and consecrated priests and teachers in the land, to baptize unto the Lord whosoever were desirous to be baptized . ( Alma 15:13)